Background This study compared clinical features of the Delta variant of coronavirus disease 2019 (COVID-19) in children and adults. Methods Clinical data included 80 children and 132 adults with the Delta variant of COVID-19, hospitalized in the Affiliated Hospital of Putian College between September and October 2021. The data was analyzed retrospectively. Results The proportion of mild patients in the children group (50%) was higher than that in the adults group (17.9%). Cough (25%, 20/80) and diarrhea (1.3%, 1/80) symptoms in children group were significantly less frequent. Compared with adults, there was no significant difference in the viral load of SARS-CoV-2 in samples collected by nasopharyngeal swabs. In children, lymphocyte count was higher [1.98 (0.25–4.25) vs 1.20 (0.29–4.27) ×109/L], whereas the interleukin-6 level was lower [5.87 (1.50–61.40) vs 15.15 (1.79–166.30) pg/mL] than that in adults group. Additionally, the incidence of liver injury in children group was lower than that in adults group. There was no significant difference in the incidence of proteinuria (22/75 vs 45/112) between the two groups, but the serum creatinine level in children was lower [42.0 (28.0–73.0) vs 57.0 (32.0–94.0) µmol/L]. Conclusion Compared with adults, children with the Delta variant of COVID-19 have differences in symptoms, clinical classification, inflammatory indices, and liver/kidney function injury. Children’s illness is relatively mild. Clinicians should pay attention to their differences and use drugs accurately.